Ab initio MCSCF/6-31G** adiabatic potential energy surfaces have been determined for both the ground and first excited states of triplet CH3+. Classical trajectory studies of the collision of C(P-3) with H-3(+)((1)A(1)') on both surfaces yield an overall rate coefficient of 2.1 x 10(-9) cm(3) s(-1) for the formation of CH+ ((3) Pi) + H-2 at 10 K, in good agreement with earlier work. A rate coefficient of 4.9 x 10(-11) cm(3) s(-1) at 10 K has been determined for the previously unknown reaction which produces CH2+((2)A(1)) + H. The properties of the reaction products are examined and the accuracy of the potential energy surfaces is investigated.